Method of making molded stems



Feb.,8, 1944. HORN METHOD OF MAKING MOLDED STEMS Original Filed Feb. 24, 1939 2 Sheets-Sheet 1 'INVENI'OR CLARENCE A. HORN,

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Feb. 8, 1944.

C. A. HORN.

METHOD OF MAKING MOLDED STEMS Original Filed Feb. 24, 1939 2 Sheets-Sheet 2 T|c.'7.. has.

0 3 3 B :r In 9 Ill/Z2 lNvEN-r'oR CLARENCE A. HORN, BY

Patented Feb. 8, 1944 UNITED STATES PATENT OFFICE 7 2,340,879 METHOD or MAKING MOLDED s'rams Clarence A. Horn, Newton, Mass., assignor to Raytheon Production Corporation, Newton,

Masa, a corporation of Delaware Original application February 24, 1939, Serial No. 258,283. Divided and this application October 26, 1939, Serial No. 301,406

4 Claims. (01. set-s1) This invention relates to electrical discharge devices comprising sealed envelopes, such as electron discharge devices and the like, and more particularly to a novel stem and a novel method of making such a stem. This application is a diviof the foregoing type which can be manufac tured in a simple, inexpensive and reliable manner.

Another object is to devis a novel method of making such a stem. The foregoing and other objects of this invention will be best understood from the followin description of an exempliflcation thereof, reference being had to the accompanyingdrawings, wherein:

Fig. l is a perspective view, partly broken away, of an electron discharge tube incorporating my novel stem;

Fig. 2 is a top view of a stem made in accordance with the present invention;

3 is a section taken along line 33 of Fig. 4 is a section taken along line 4-4 of i 2;

Fig. 5 is a perspective view of the top press block of a machine for molding my novel stem;

Fig. 6 is a perspective view of the bottom press block of such a machine, said figure being placedv in juxtaposition to Fig. 5 in order to show their relative operating positions; and

Figs. '7, 8 and 9 show essential parts of the machine for molding my novel stem and the successive steps in forming such a stem. 7

The tube as illustrated in Fig. 1 consists of a glass envelope 1 having a bottom wall consisting of a stem or base 2. A plurality of lead-in rods 3 are sealed through said stem 2. These lead-in rods are made of some metal which readily seals to the glass of said stem, and may conveniently be made of chrome iron. The lead-in rods 3 are disposed in a circle concentric with the center of the stem 2. These lead-in rods are also rigid so that in the completed form of wthe tube they serve as the external contact pins adapted to be inserted into a cooperating tube socket. If desired a number of dummy support wires 4 may likewise be sealed into the upper surface of the stem 2. These dummy support .wires do not extend through the stem, and

therefore need not form an air-tight seal therewith. For this purpose thesedummy support wires may be made of a metal which does not make a perfect seal with the glass. They may conveniently be formed of nickel. The usual type of mount 5 is supported by the lead-in rods 3 and the dummy support wires 4. The mount 5 may consist of a plurality of electrodes, for example,

an anode 8 surrounding a cathode I. .In order to enable the tube to be exhausted, the stem 2 is provided at its central portion'with an exhaust opening communicating with an exhaust tube 8. The bottom of the tube is surrounded by a guard shell 9 held in place on the tube by means of a ring of cement Ill. The guard shell 9 is provided with a central tubular member ii which surrounds and protects the portion of the exhaust tube remaining on the completed tube. The guard shell 9 is provided with sufficiently large openings around each of the lead-in rods 3 so that electrical contact between the shell 9 and the rods 8 is effectively prevented.

The tube, as illustrated in Fig. l, is adapted to be inserted in a suitable tube socket, the tubular member ll cooperating with some suitable look:- ing arrangement, and the pins 3 cooperating with suitable contact members in said socket, whereby the proper electrical connectionsmay be made to the electrode elements within the envelope fl. A tube of the foregoing type presents certain diiiiculties and requirements if such an arrangement is to be commercially successful. Since the lead-in rods 3 serve as the external contact members for the tube, they must be kept parallel and maintained accurately in their predetermined circular relationship in order that such tubes may fit interchangeably in standard sockets provided therefor. The glass of the stem must not extend too far up or down along the lead-in rods 3. Glass extending down along the lead-in rod might well interfere with the proper insertion of the tube into its socket. Glass extending along said rod 3 in either direction to an excessive degree produces a tendency for cracks to occur at the lead-in rods. Another requirement is that the stem 2 may be easily sealed to the envelope 5 by the usual type of sealing-in machine. A further requirement is that during this sealing-in process, the main body of the stem 2 carrying the lead-in rods 3' shall not be subjected to any distortion which might tend to upset the requisite positional accuracy of said lead-in rods. Stems made in accordance with my present; invention satisfy each of these requirements, and produce a a tube which satisfies all of the objects of my intion must be sufficiently strong to withstand atmospheric pressure exerted on its lower flat surface upon completion of the tube. It must also be thick enough to firmly and definitely support the lead-in rods 3 and the dummy wires 4 without cracking. It also must be sufficiently massive so that during the sealing of the stem to the envelope it is not heated sufficiently to soften to any appreciable extent. I have found that the thickness of this central portion in a particular instance conveniently may be between .080 and .095 of an inch. However, thicknesses as low as .060 might be feasible in some instances. Surrounding the thickened portion I2 is a thinned edge l3. The top of this edge I3 is preferably disposed in the same plane as the top of l2, for reasons which will be explained below. This thinned edge l3 must have a thickness sufliciently less than that of the central portion l2, so that during the sealing-in process it can soften sufficiently to seal readily to the glass envelope without producing any appreciable softening of the central portion I2. I have found that the thickness of the edge l3 conveniently may be made about half of the thickness of the central portion I2. In a particular instance I have used .045 to .055 as a thickness of said edge. In the particular examples which I have cited, the thickness of the wall of the glass envelope I was between .030 and .050 of an inch. The stem 2 is preferably formed with a lower boss |'4 around each lead-in rod 3, and a smaller upper boss l5 around each of said lead-in rods. The bosses l4 project through the openings in the guard shell 9, and thus maintain said guard shell in its proper position as well as insure against electrical contact between said guard shell and the lead-in rods.

In Figs. 5 and 6 I have shown certain essential features of the machine for molding the novel stem describedabove. In Fig. 6 there is shown the lower press'block l6v which is provided with a central circular depression I! which forms the lower press mold. The face ,of the lower press mold is provided with a plurality of holes I8 adapted to receive the rods 3. Said lower press mold is also provided with a plurality of holes l9 which are adapted to receive the dummy support wires 4. The surfaces of the lower press mold around each of the holes l8 and I9 are recessed in order to provide boss-forming surfaces. Around the circular depression I! is provided a raised edge 20 which forms a stop beyond which the molten glass during the molding operation cannot flow. This edge, therefore, determines the maximum diameter of the edge l3 of the stem. In Fig. 5 is shown the upper Dress block 2| likewise provided with a central circular depression 22 which forms the upper press mold. This upper press mold is provided with holes 23 only for the rods 3, since as previously indicated the dummy support wires 4 do not extend through the press 2. The upper press mold likewise is recessed around each opening 23 in order to provide boss-forming surfaces. The upper press mold is provided with a central hole 24 for the purpose of receiving the exhaust tube 8, while the lower press mold is provided with a central opening 25 through which an exhaust-forming mandrel may project. The upper press block 2| is also provided with a raised edge 26 surrounding the upper press mold depression 22. This raised edge 28 is of smaller diameter than the raised edge 20, and determines the diameter of the central thickened portion l2 of the stem. These differences in diameter likewise form the thinned edge II as will be evident from the following description of the mode of manufacture of said stem.

. Figs. '7, 8 and 9 show the relative operative positions of the upper and lower press blocks I6 and The lower press block I6 is mounted to rotate in a fixed plane, while the upper press block is suitablymounted to reciprocate in a vertical line above the lower press block. The upper block 2| is also mounted to rotate in synchronism with said lower press block.

The glass for the stem is supplied in the form of two glass rings or collars 21 and 28, which as shown are. set upon the lower press block l5, respectively, inside and outside of the circle of holes |8 and IS. The lead-in rods 3 are then threaded into the openings l8, and the dummy support wires 4 are threaded into the holes IS. The inner glass ring is formed, as shown, with the top portion 29 thereof turned in so as to rovide a substantial amount of glass already positioned toward the central portion of the stem. This arrangement facilitates the uniform distribution of glass throughout the extent of the stem, and also prevents the melting and sticking of glass onto the rods 3 above the maximum desired height. This latter tends to occur when straight glass rings of the requisite size are used. The turned-in shape of the inner glass ring 28 also facilitates the guiding or threading of the rods 3 and wires .4 into their respective holes l8 and |9. The exhaust tube 8 is also inserted into theopening 24 so as to be in a position to be sealed to the stem.

Heat may be conveniently applied to the glass from gas burners 30 positioned to play on the upper rims of the glass rings. As the glass collars soften, their upper edges flow together and around the lead-in rods and wires to form a plastic mass which adheres to the wires, as shown, for example, in Fig. 8. To sufficiently soften the glass and minimize the tendency of said glass to stick to the lower press mold IS, the lead-in rods 3 and the adherent mass of glass are then raised above the lower press mold l6, as shown in Fig. 8. For this purpose a plunger 3|, provided below the lower press block I6, is raised, pushing the lead-in rods and glass upwardly into the direct path of the gas flames. After the mass of glass has become sufficiently plastic, the upper press block is lowered, and with the downward movement of said press block, the molten glass is molded between the two blocks 2| and IE to form the requisite shape of stem as previously described. The holes 23 in the upper press block 2| are made of limited depth so that, during the above molding operation, they come into contact with the upper ends of the lead-in rods 3. During said molding operation, the plunger 3| is retracted in synchronism with the downward movement of the upper press block 2|. This results in the lead-in rods 3 being pushed through the mass of plastic glass. This motion insures an exact limitation of the degree to which the glass extends along the lead- Various changes will sug est themselves to form of said bosses, therefore, is usually slightly recessed around the rods}, as shown more clearly in Fig. 4. This particular step insures a remarkable uniformity of the size and position of said bosses ll. During the foregoing molding operation, the-exhaust tube the lower end of which previously has been softened by the applicationof a gas flame thereto, is broughtinto contact with the central portion of the plastic sures an accurate alignment of the various elements of the completed stem. The completed stem is then removed from the machine.

After the stem has been completed, the mount is assembled on the lead-in rods 3 and dummy support wires 4. The envelope l is then sealed in rods 3 to form the bosses ll. The resulting glass to form a stem with said conductor extendin: on both sides of said stem, and moving said lead-in conductor substantially along its longitudinal axis to a limited extent through said fused mass of glass. v

2. The method of forming, a molded glass stem which comprises assembling two coaxial glass rings, inserting lead-in conductors through the annular space defined by said rings, heating said rings to fuse them together around said conductors, pressing said fused rings into a substan- V tially flat disk-shaped stem with said conducto the stem around the mount along a sealingin point 46, This envelope is conveniently positioned by resting against a pair of standards 43 formed as part of the mount 5.

Of course it is to be understood that this invention is not limited to the particular details 7 as described above as many equivalents wili' suggest themselves to those skilled in the art. For example, in some instances it may be desired to.

utilize this invention in tubes having the conventional base with additional contacting prongs. those skilled in the art.

what is claimed is: 1. The method of forming 'a molded glass stem which comprises fusing a mass of glass around a lead-in conductor, pressing said fused mass of tors extending on both sides of said stem, and moving said lead-in conductors substantially along their longitudinal axes to a limited extent through said fused mass of glass.

3. The method of forming a molded glass stem which comprises fusing amass of glass around a lead-in conductor, pressing said fused mass of glass to form a stem with said conductor extending on both sides of said stem and with a projecting boss formed around said lead-in conductor, and moving said lead-in conductor substantially along its longitudinal axis to a. limited extent through said fused mass of glass in a direction to depress the outer end of said boss.

4. The method of forming a molded glass stem which comprises assembling two co-axial glass rings, in'se'rtinglead-in conductors through the annular space defined bysaid rings, heating said rings to fuse themtogether around'said' conductors, pressing said fused rings into a substantially flat disk-shaped stem with said conductors extending on both sides of said stem and with a projecting boss formed around each of said conductors, and moving said lead-in conductors, substantially along their longitudinal axes to a limited extent through said fused mass of glass in a direction to depress the outer end of each of said bosses. I

CLARENCE A. HORN 

